334 The Ohio Naturalist. [Vol. V, No. 7, 



Suppose that this spore, on germination, fails to reduce the 

 chromosomes. The resulting individual will have the double 

 number in each cell. Now if, when reduction takes place, the 

 cells reduce the chromosomes and the resulting cells are gametes, 

 a new condition arises in which a "2a:" sexual generation orig- 

 inated from an ":r" nonsexual type gives rise to gametes as the 

 result of a reduction division. A simple sexual cycle is estab- 

 lished with a "2x" sexual generation producting gametes as the 

 result of reduction (Fig. 1 b). Such plants as Fucus must have 

 established their life cycle in this way. The Fucus plant is a 

 2x sexual generation which develops ovaries and spermaries. A 

 cell in the ovar}^ undergoes the reduction division and by further 

 divisions usually produces eight eggs with x chromosomes each. 

 In the spermaries a cell also undergoes reduction and by subse- 

 quent divisions a number of spermatozoids are produced having 

 the X number of chromosomes. 



3. The third point at which the reduction division may be 

 established is after the sporophyte stage in connection with an 

 alternation of generations. Suppose a nonsexual organism 

 develops zoospores which conjugate and the zygote fails to reduce 

 the chormosomes at the first division. An individual is produced 

 with 2x chromosomes. When zoospores are produced as the result 

 of a reduction division they come out not as gametes but as non- 

 sexual spores which give rise to an x generation. This genera- 

 tion being similar to the original generation produces gametes 

 without reduction which have the x number of chromosomes. This 

 is the process in the plants with a true, antithetic alternation of 

 generations. A gametophyte generation is followed by a sporo- 

 phyte generation which reduces the chormosomes before the 

 development of nonsexual spores (Fig. 1 c). 



Other life cycles might be and perhaps are developed. A 

 sporophyte coming from the z3"gote might develop spores with- 

 out reduction and these might develop into gametophytes with 

 the 2x chromosomes, and the gametes would then be produced 

 as the result of a reduction division (Fig. Id). It will be yeen, 

 therefore, that there are two types of sexual or gamete-producing 

 generations, one with the 2x chromosomes giving rise to gametes 

 through reduction, the other with x chromosomes giving rise to 

 gametes directly without reduction. 



Now in the higher plants the life cycle is invariably estab- 

 lished, unless in abnormal cases, with an alternation of genera- 

 tions, a gametophyte generation with x chromosomes is followed 

 by a sporophyte generation with 2a: chromosomes. The reduc- 

 tion division takes place in special cells, sporocytes, and usually 

 by two successive divisions. The resulting spores have the 

 reduced number of chromosomes and represent the first cell of 

 the gametophyte generation (Fig. 2). There is no more reason 



